1. Field of the Invention
This invention relates to a method for and an apparatus of thermal treatment of human waste, and more particularly to a method for and an apparatus of thermal treatment of human waste which is compact and efficient and which can be used for vehicle toilets, movable toilets, etc.
2. Description of the Prior Art
Heretofore, there have been known a water treatment method and a thermal treatment method, as an ordinary method for treating human waste, which uses a heating power. The thermal treatment, when compared with the water treatment, has such advantages as that only a small quantity of ash is produced and no exhaust water is produced and thus sanitary. Therefore, many self-governing communities adopted this method. With this thermal treatment method, the self-governing communities can easily get an amicable consent from local inhabitants for establishing such human waste treating facilities.
However, the conventional thermal treatment method of human waste has such an disadvantage as that a large quantity of fuel is consumed. Therefore, some enterprises, that employed the conventional thermal treatment method, were obliged to cease operation for a while because of an economical reason. In order to overcome these inconveniences, many attempts have been made for improving the thermal efficiency of such system in various fields. As one reason for lowering the thermal efficiency in the conventional method, it has been pointed out that human waste contain some elements for producing an offensive smell gas other than water, besides its structural problem that thermal losses caused by heat dissipation are not sufficiently utilized. In other words, there are two reasons for the conventional thermal treatment apparatus of human waste consuming a large quantity of fuel. One reason is that a moisture contained in the human waste is required to be evaporated, and the other reason is that an evaporated vapor containing elements for an offensive smell is required to be combusted again in order to remove the offensive smell. The ratio of the heat consumption by the above two reasons is found to be about 20% of an intaken heat through a trial calculation.
The quantity of heat consumption in an average thermal treatment apparatus will be shown hereunder.
The quantity of heat for incinerating 1 kg of human waste is as follows.
In the case of a heavy oil: It requires 3005 kcal and 0.307 kg is consumed during combustion for a period of five minutes.
In the case of an electric power: It requires 2652 kcal and 3.7 kw is consumed during combustion for a period 20 minutes.
Let us hereby review a temperature distribution and a heat balance in a rotary kiln system as an ordinary method for treating human waste. Given that an average specific heat at constant pressure of a mixed gas including an exhaust gas and a water vapor generated by means of combustion of a heavy oil at a temperature of 500.degree. C..about.800.degree. C. is 0.274, the quantity of exhaust gas generated by means of combustion of a heavy oil is 14 Nm.sup.3 /kg, the heating value of a heavy oil is 9800 cal per unit weight, and the thermal efficiency is 36.4%, as the heat intaken by means of an evaporating burner is 3005 kcal/H.sub.2 O.kg, the quantity of a thermal gas of the heavy oil becomes as follows. EQU (3005.div.9800).times.14=4.3 Nm.sup.3 /H.sub.2 O.kg
Given that the latent heat is 539, the temperature, the quantity of heat and the capacity of the mixed gas within the rotary kiln become as follows.
Capacity: 1.244+4.3=5.54 Nm.sup.3 /kg PA0 Quantity of heat: (3005.times.0.364)-539=555 kcal/5.6Nm.sub.3 PA0 Temperature: 555.div.(5.5.times.0.274)=368.degree. C.
Also, the quantity of heat for raising temperature and the capacity of gas which are required for removing the offensive smell is as follows.
Since 5.5.times.(800-368).times.0.274=651 Kcal/5.5Nm.sup.3
Quantity of heavy oil: 651.div.9800=0.066 kg PA1 Quantity of heavy oil gas: 0.066.times.14=0.924 Nm.sup.3
From the foregoing, given that the thermal efficiency is 36.4%, it requires the following quantity of heat in order to incinerating 1 kg of human waste. EQU (619+651).div.0.364=3489 kcal
In this way, a gas, which is generated when human waste are evaporated by means of direct heating, is a sum of a combustion gas and an evaporation gas. Therefore, as the capacity of an offensive smell gas, the smell of which is required to be removed by means of oxidation, is increased, the quantity of heat consumed for increasing the temperature of the whole offensive smell gas is increased and thus, an economic burden is increased. In addition, there are the following problems.
1. As it is difficult to form a high combustion temperature zone of 800.degree. C., a non-oxidized gas is flowed out.
2. It is unavoidable to enlarge facilities in order to cope with the increased capacity of the offensive smell gas.
3. A large power is required in order to circulate the offensive smell gas including a combustion gas and an evaporation gas within the apparatus until the gas is discharged into atmosphere.
4. As it is difficult to completely seal the rotating portions of the seal type apparatus because of durability or structure, a leakage of gas is easy to occur.